1. Field of the Invention
This invention relates generally to veterinary obstetric devices. More particularly, but not by way of limitation, this invention relates to devices useful in removing the animal fetus during vaginal delivery.
2. Prior Art
Cattle, horses and sheep normally deliver their young vaginally. Complications arise in livestock births just as complications arise in the births of humans. For example, in approximately 10-25% of the births of calves, traction is required. One can expect a similar traction requirement in the births of foals and lambs. Traction is the application of force to the presenting parts of the animal fetus in order to supplement or replace the natural maternal forces in removing the animal fetus from the uterus of the animal mother. Presenting parts are those parts of the animal fetus nearest the vaginal opening of the animal mother.
The following description of livestock delivery is intended as generic to bovine (cattle), equine (horses), and ovine (sheep) deliveries. In a normal presentation (i.e. positioning) of the fetus, the presenting parts are the forelegs (i.e. front legs) and head of the animal fetus. The forelegs appear first, heels down, with one foreleg slightly in front of the other; and the head is between the forelegs. In human deliveries, the mother experiences the greatest difficulty in passing the head through the birth canal. In livestock deliveries, the mother animal typically experiences the greatest difficulty in passing the shoulders through the birth canal because the shoulders are the widest part of the animal fetus's body.
If the animal mother appears to be straining but not progressing in expelling the animal fetus, traction may be required. The prior art reveals several robust, if not crude, traction implements including chains, cords, snares, hooks, tongs, cutters, and winch-type or rachet-type mechanical extractors. All of these devices are used to apply traction force to the forelegs or the head, or both, of the fetus.
The most common device used for applying traction to the forelegs is the Moore's chain. A Moore's chain typically consists of a length of steel chain with a large closed steel ring connected to the last link at each end of the chain. Each of these closed steel rings is of sufficient size to allow a portion of the chain to be wrapped around the animal fetus's foreleg and passed back through the ring. The chain operates on the same principle as a dog choker-chain. When a dog choker-chain is pulled along its length, the loop around the dog's neck is tightened. In the use of a Moore's chain, each end of the chain is used to form a loop around each foreleg of the fetus. A handle or a mechanical traction device is attached to the approximate midpoint of the chain and traction force is applied, thereby tightening each loop around the two forelegs of the animal fetus and pulling the forelegs out of the mother animal. There are other devices, similar to the Moore's chain, which work using the choker-chain concept but employ cord, rope, or cable instead of chain.
Normally when traction is indicated it is applied simultaneously to the forelegs and the head; although traction may initially be applied to the forelegs alone until the head becomes accessible. Devices for applying traction forces to the head consist of various cables, cords, or ropes which are looped around the head. One commonly used device, known as a cable head puller, comprises a steel wire cable which is looped around the animal fetus's head just below the ears. After looping around the animal fetus's head, the two ends of the cable pass through a metal locking slide which holds the loop tightly around the animal fetus's head. The metal locking slide works in a way similar to a western-style string tie. The metal locking slide also has a portion which engages the teeth of the animal fetus. The two cable strands pass through the metal locking slide and terminate, joined together, in a yoke at the end of the cable. The yoke can be connected to a handle for applying human traction or the yoke can be connected to a mechanical traction device. Traction can be applied to the cable head puller alone or the cable head puller and the Moore's chain can both be connected to a handle or a mechanical traction device.
The design emphasis of the Moore's chain and devices similar to it has been toward ensuring an effective grip on the animal fetus. Little consideration appears to have been given toward minimizing the translation of the pulling and gripping forces into blunt trauma of the animal fetus and the animal mother. An additional shortcoming of the Moore's chain is that the foreleg is turned in the birth canal because the chain loops exert forces not aligned with the axis of the birth canal. This misdirected force causes an even wider cross-section of the presenting parts of the animal fetus in an animal mother who is already unable to naturally expel the animal fetus.
When using Moore's chains, the likelihood of injury is high because of the great forces used in traction. One skilled in the art will know that the force of four average men will usually be required to extract the animal fetus in a traction-assisted birth. Accordingly, fetal and maternal injuries are fairly common in traction-assisted births. The injuries can result in death of the animal fetus or animal mother, fetal limb loss, or fetal treatment for secondary infections resulting from injuries incurred in delivery.
Regardless of the extent of the injury, the net result for the cattle, horse, or sheep rancher is ranch hand time lost on treatment of birth injuries or secondary complications. In many cases veterinary intervention may be required, which will cost the rancher additional money. The need for a veterinary traction device which reduces trauma is motivated not only by cost savings, but also by compassion for the animal fetus and the animal mother.
The Moore's chain can also cause human as well as animal injury. As mentioned earlier, it is known in the art that the force of four average men will be necessary to replace the maternal forces. Because of the force required, in cases in which mechanical traction cannot be used or a mechanical traction device is not available, more than one assistant is involved. It is simply not possible for four assistants to fit their hands on the handle. Therefore, it is common for the assistants to grab a portion of the Moore's chain near the point where the Moore's chain is connected to the handle. Often the assistants' hands are pinched in the chains or the assistants are limited in the amount of force they can apply because of the pain suffered from grabbing a steel chain.
The Moore's chain and other similar devices which use the choker-chain concept have at least one other significant drawback. Such devices remain securely wrapped about the forelegs only when traction force is applied. If the traction force is interrupted for any reason, the gripping force is also interrupted. The loops on the forelegs can then slip to an improper position or come off completely, requiring a human assistant to reposition the chain.
This failure to securely hold the foreleg when slack is also significant when the choker-chain type devices are put to their secondary use, weighing the newborn animal. To weigh the newborn animal, one Moore's chain is looped around the newborn animal's forelegs, and a second Moore's chain is looped around the hindlegs (i.e. back legs). The chains are gathered together at their approximate midpoints and hooked to a scale so that the newborn animal is suspended in mid-air.
Those skilled in the art will know that the newborn animal is usually uncooperative in this venture. Significant ranch hand time is wasted subduing the newborn animal long enough to hook up the Moore's chain or a similar device. With the slightest interruption in the pulling force, the loops on the forelegs and hindlegs loosen and an uncooperative newborn animal can extract one or more of its legs from the chains.
Examples of current veterinary devices include U.S. Pat. No. 3,643,664 entitled "Dual-Pull Veterinary Fetal Extractor" issued on Feb. 22, 1972 to Robert L. McMillan; U.S. Pat. No. 3,183,911 entitled "Fetal Extractor" issued on May 18, 1965 to Alfred A. Anglemyer; U.S. Pat. No. 3,955,582 entitled "Obstetrical Tool For Animals" issued on May 11, 1976 to Richard C. Pierce; and U.S. Pat. No. 4,502,486 entitled "Device For Veterinary Obstetrical Delivery" issued on Mar. 5, 1985 to Werner Weiland. Human traction devices include U.S. Pat. No. 3,550,595 entitled "Obstetrical Forceps" and issued on Dec. 29, 1970 to Leonard E. Laufe; U.S. Pat. No. 3,605,748 entitled "Obstetrical Forceps" and issued on Sep. 20, 1971 to Hector Salinas-Benavides; U.S. Pat. No. 3,665,925 entitled "Obstetrical Forceps" and issued on May 30, 1972 to Hamo M. Dersookian; U.S. Pat. No. 3,785,381 entitled "Pressure Sensing Obstetrical Forceps" and issued on Jan. 15, 1974 to Brenton R. Lower et al; U.S. Pat. No. 3,789,849 entitled "Obstetrical Forceps" and issued on Feb. 5, 1974 to Leonard E. Laufe et al; U.S. Pat. No. 3,794,044 entitled "Delivery Forceps" and issued on Feb. 26, 1974 to William O. Vennard; U.S. Pat. No. 5,122,148 entitled "Device For Assisting Childbirth" issued on Jun. 16, 1992 to Gary E. Alexander; and U.S. Pat. No. 5,217,467 entitled "Device For Assisting Childbirth" issued on Jun. 8, 1993 to Gary E. Alexander.